The present invention concerns an electric or electronic component, particularly an electric or electronic circuit or a non-volatile memory.
It also concerns the application of such a component as a non-volatile memory and as a device with acoustic surface waves.
During the last decade, rapid progress has been made in the deposition of films with composite epitaxial, oxide-base structures, laying the groundwork for subsequent advancement in the field of copper oxide superconductors and allowing preparation of epitaxial films of materials such as magnetoresistant manganese oxides. One of the numerous other families of materials recently formed using this epitaxial approach is ferroelectric oxide. One attractive quality of these materials is their reversible, non-volatile polarization field. In addition, numerous devices with electric field effects have been developed, ranging from dynamic random access memories (DRAMs) to nanosystem models such as dual dimension electronic gases.
All these devices require the use of permanent metal electrodes to produce and maintain the electrical field, which poses a major problem because very delicate lithography is required to manufacture the metal electrodes.
U.S. Pat. No. 5,206,525 describes a device essentially equivalent to a field effect transistor with the dielectric replaced by a pi-conjugated macromolecular material mixed with a ferroelectric material. The goal of this invention is to modify conductivity using the electrical field. However, this device cannot modify local electronic properties.
U.S. Pat. No. 5,371,729 describes a data storage device based on the principle of locally commutating the polarization of a ferroelectric film deposited on a semi-conductor. The aim of this invention is to increase working speed by using high voltage current to generate an avalanche phenomena.
European Patent Application published as No. EP-O 275 881 describes a device which uses a tunnel effect microscope to read and write data on an electrically polarized film, which is primarily a polymer. The purpose of this device is not to write data using electrical impulses or to read data by detecting local modifications in electronic density.
The present invention proposes a novel electric or electronic component which either simplifies both the permanent electrodes and the customary lithography manufacturing process, or renders them completely superfluous. In addition, the method of making this component is non-invasive.
This goal is achieved by the component according to the invention, characterized in that is comprises a composite structure consisting of least one layer of ferroelectric material and at least one semi-conductor or a thin film of a metal or superconductor material, in close contact with at least one surface of said layer of ferroelectric material, as well as means for generating local polarization modifications in said ferroelectric layer either to cause local modifications, on a scale ranging from nanometers to micrometers, in the electronic density of one zone on said semi-conductor or of the thin metal film or of the superconductor, said zone being close to said surface of said ferroelectric layer; or to use a piezoelectric effect to create a local deformation in said layer of ferroelectric material, depending upon the polarization value, in order to generate an acoustic surface wave.
According to its preferred embodiments, said means for generating local polarization modifications in said layer of ferroelectric material may comprise a device for applying current between at least one selective electrode, designed to selectively scan the surface of said composite structure opposite the surface consisting of the semi-conductor or thin film of metal or superconductor material, and said semi-conductor or thin film of metal or superconductor material.
According to an advantageous embodiment, said composite structure may consist of a semi-conductor or a thin film of metal or superconductor material in close contact with a first surface of said layer of ferroelectric material, and a very thin film of semi-conductor, metal, or superconductor material in close contact with a second surface of the layer of ferroelectric material which is opposite said first surface of the layer of ferroelectric material.
According to this embodiment, the surface of the composite structure that is scanned or swept by a selective electrode is the very thin semi-conductor, metal, or superconductor film which is in close contact with the second surface layer of ferroelectric material, with current being applied between said selective electrode and said very thin film. Current may also be applied between the electrode and the semi-conductor or the thin film of metal or superconductor material in close contact with the first surface of said layer of ferroelectric material. In both these cases, it is possible to apply current simultaneously between said very thin semi-conductor, metal or superconductor film and the semi-conductor or the thin film of metal or superconductor.
Advantageously, said selective electrode may consist of the tip of a microscope with a local sensor. It may also consist of a source of particles.
According to a first embodiment, said particle source is designed to generate an electron beam.
According to a second embodiment, said source of particles is designed to generate an ion beam.
In a variation, said selective electrode may consist of a radiation source.
In a particularly advantageous embodiment, the polarization of said layer of ferroelectric material is represented by a characteristic that is sensitive to local modifications in the electronic density of said semi-conductor or in the thin film of metal or superconductor material.
Preferably, said characteristic is the tunnel conductance between a local wave scanning the surface of the composite structure opposite the surface constituting the semi-conductor or the thin film of metal or superconductor material, and said semi-conductor or thin film or metal or superconductor material.
One of the particularly advantageous applications of the component is in the formation of an acoustic surface wave device, specifically, a filter for frequencies typically ranging up to 20 GHz and higher.
Another application of the component is to use it as an electronic circuit, particularly as a non-volatile memory.